1. Field of the Invention
The present invention relates to a programmable timer circuit that can be connected directly to the fan switch of any thermostat with a forced air heating and/or cooling system that includes a blower fan for circulating air throughout the home. The present invention also relates to a programmable timer circuit that can be connected directly to any thermostat used in a hot-water heated home with a boiler and pump for circulating hot water through the heating system.
2. Description of the Related Art
In homes that use an auxiliary heat source such as a wood, gas or pellet stove or a fireplace, the air in the room in which the heat source is located can become quite warm while the temperature in the rest of the home is exceedingly cool. This temperature differential can be uncomfortable to the homeowner. In the case of a home with hot-water-based heat, including radiant and/or baseboard heat, and an auxiliary heat source, the thermostat can report that the main part of the home is sufficiently warm and never call for hot water to circulate through the system, even though other parts of the home are quite cool. This circumstance can cause pipes associated with the heating system to freeze and burst because the water in them is never circulated. The present invention solves both of these problems by periodically circulating hot air or hot water, depending upon the home's heating system, throughout the home.
Mobile home owners experience similar problems. The pipes for mobile homes run underneath the home and receive heat from the furnace. If the mobile home has an auxiliary heat source, the thermostat never calls for heat from the furnace. In that event, the water pipes can freeze and burst because they are not receiving warm air from the furnace. The present invention periodically circulates the air from inside the mobile home to the area underneath the home, thereby preventing the pipes from freezing.
There are a number of patented inventions that relate generally to furnace or air conditioning control systems, but none that provides the unique features and ease of use of the present invention. For example, U.S. Pat. No. 4,838,482 (Vogelzang, 1989) discloses an air temperature conditioning system comprising a thermostat, a remotely located air temperature conditioning apparatus, a circuit means of connecting the thermostat to the air temperature conditioning apparatus, a fan connected to the conditioning apparatus, and a cycling means that is connected to the fan and that is controlled by a switch on the thermostat. The patent also provides an improvement in a space temperature control system wherein a remote temperature conditioning apparatus is controlled by a manual switch on the thermostat, the fan operates independently of the temperature conditioning apparatus, and a circuit means is connected to the manual switch to allow the fan to operate even when the temperature conditioning apparatus is not operating. Unlike the present invention, the invention covered by the Vogelzang patent cannot be retrofitted to an existing thermostat, and it requires wiring modifications that the present invention does not.
U.S. Pat. No. 4,842,044 (Flanders et al., 1989) provides a heating and cooling control system that works by energizing a fan or other fluid circulating device to circulate fluid and effect thermal transfer of energy from the fluid to the spaces being heated and by deenergizing the circulating means at a selected time interval after deenergization of the heating and control system. The patent also claims a heating control system comprising a switching means to effect energization of the fluid circulating means, a switching control means that is energizable in response to operation of the control circuit, and an additional circuit means that energizes the switching control means a selected time interval after deenergization of the heating system. The invention covered by this patent is intended to increase the time the fan is turned on after a heating cycle to improve energy efficiency. It is distinguishable from the present invention because it does not periodically circulate the blower, and it also requires the breaking of the fan circuitry. It also draws power continuously from the gas solenoid through a 680 ohm resistor, and this method has proven to be problematic in practice. The invention cannot be used to keep pipes from freezing in a boiler system, whereas the present invention can.
U.S. Pat. No. 5,142,880 (Bellis, 1992) discloses a solid state control circuit for use in connection with existing low-voltage thermostat terminals of a central, forced-air, air conditioning system having a compressor and an indoor blower and gas-fired or electrical heating elements. The invention relates generally to systems for increasing the efficiency of air conditioning units by continuing the blower running time after the compressor is turned off. Specifically, the patent claims an air conditioning control unit comprising a low voltage room thermostat fan terminal, a low voltage compressor relay terminal, a timing circuit means, a sensitive gate triac, and a power triac. The patent also claims a method for controlling the on-off time of an indoor fan that is controlled by and associated with an indoor thermostat for a room air conditioning system. This invention is distinguishable from the present invention because it does not cycle the fan but only lengthens the duration after a heat cycle. In addition, this invention, like the Flanders invention, has to be inserted into the existing circuit and thus can cause problems with the heating and cooling system if it fails.
The invention described in U.S. Pat. No. 5,547,017 (Rudd, 1996) is a system for controlling the operation of the circulating fan of a closed central air conditioning (CAC) system. The system periodically activates and deactivates only the circulating fan after a preselected delay time from the normal running of the cooling and heating modes of the CAC system, and the cooling and heating modes of the CAC system operate independently of the fan recycling control. This invention differs from the present invention because it requires connection to the air circulation system, whereas the present invention only requires connection to the thermostat. Furthermore, the timer function of the Rudd invention is not user programmable, but the timer of the present invention is.
U.S. Pat. No. 5,582,233 (Noto, 1996) relates to a timer circuit and power outlet control circuit for augmenting control and regulating operation of the blower fan in a forced air heating and cooling system. The only independent claim covers an improvement to existing technology comprising coupling a timer device into a forced air heating and cooling system and programming the timer device to delay cessation of the blower fan operation and to maintain the blower fan in operation for a limited finite time period after the cooler or heater ceases operation. Unlike the present invention, this invention is not user programmable, and it has no user interface. It requires insertion of the invention into the circuit by re-routing the wire that normally connects to the fan switch. It requires a power source and, therefore, cannot mount directly to the thermostat. Another difference between this invention and the present invention is that the present invention entails only two wires, and the wires can be connected on either side of the fan switch (in other words, each terminal on the unit is interchangeable). With the Noto invention, the wires need to be connected in a certain way to certain terminals.
In U.S. Pat. No. 6,318,639 (Toth, 2001), the inventor describes an electronic programmable thermostat with different modes of fan operations, including an automatic mode, a time mode, and a continuous mode. In the automatic mode, the air-circulating fan is operated based on temperature-related demands of the climate control system. In the time mode, the fan is operated based on the time of day. In the continuous mode, the fan is operated continuously. The invention is an improvement comprising a user-selectable temporary fan-on mode of operating the air-circulating fan in which the air-circulating fan is operated only once for a pre-selected period of time. Once the fan runs for a predetermined amount of time, operation of the fan returns to being controlled by a regular thermostat. Whereas the present invention is an addition to an existing thermostat, the Toth invention is a thermostat device. The device provides a temporary period of operation, not periodic cycling as with the present invention.
Finally, U.S. Pat. No. 6,572,338 provides a modular timer for an air circulator that energizes an air circulator motor for a predetermined amount of time. A selector switch controls the timer setting of the timer such that the time period corresponds to at least one time period of a work shift. This patent relates to a timer that attaches to an external fan and is not connected to a thermostat as part of the heating/cooling system. The present invention attaches to the thermostat and becomes part of the heating/cooling system.
The main objects of the present invention are:
(1) to provide a thermostat or boiler timer device that does not require any special power connection;
(2) to design the device such that each terminal on the unit is interchangeable for purposes of connecting the device to the fan or thermostat switch;
(3) to eliminate the necessity of any wiring modifications to accommodate the device; and
(4) to restart the timing cycle automatically when the thermostat calls for heat or cooling on its own.